1. Field of the Invention
The present invention relates to process and system for converting thermal energy from moderately low temperature sources, especially from geothermal fluids, into mechanical and/or electrical energy.
More particularly, the present invention relates to a process and system for converting thermal energy from moderately low temperature sources, especially from geothermal fluids, into mechanical and/or electrical energy including high pressure and low pressure circuits, where all partially condensed liquid from the high pressure circuit is combined with the stream coming from the low pressure circuit forming a lean stream which can be condensed at a pressure lower than a pressure required to condense the stream had its composition not been made lean or its concentration lowered.
2. Description of the Related Art
Prior art methods and systems for converting heat into useful energy at well documented in the art. In fact, many such methods and systems have been invented and patented by the inventor. These prior art systems include U.S. Pat. Nos. 4,346,561, 4,489,563, 4,548,043, 4,586,340, 4,604,867, 4,674,285, 4,732,005, 4,763,480, 4,899,545, 4,982,568, 5,029,444, 5,095,708, 5,440,882, 5,450,821, 5,572,871, 5,588,298, 5,603,218, 5,649,426, 5,822,990, 5,950,433 and 5,593,918; Foreign References:7-9481 JP and Journal References: NEDO Brochure, xe2x80x9cECO-Energy City Projectxe2x80x9d, 1994 and NEDO Report published 1996, pp. 4-6, 4-7, 4-43, 4-63, 4-53, incorporated herein by reference.
Although all of these prior art systems and methods relate to the conversion of thermal energy into other more useful forms of energy from moderately low temperature sources, all suffer from certain inefficiencies. Thus, there is a need in the art for an improved system and method for converting thermal energy from moderately low temperature sources to more useful forms of energy, especially for converting geothermal energy from moderately low temperature geothermal streams into more useful forms of energy.
The present invention also provides a method and a systems for implementing a thermodynamic cycle including a higher pressure and a lower pressure circuit, where one novel feature of the system or method involves combining a separated spent liquid stream from the higher pressure circuit with a spent stream from the lower pressure circuit prior to the condensing steps. Because the separated spent liquid stream has a leaner composition than the initial fully condensed working fluid, the stream can be condensed at a lower pressure and then combined with the separated vapor from the higher pressure circuit to form the fully condensed initial working fluid liquid stream.
The present invention provides a method for implementing a thermodynamic cycle to convert a greater amount of thermal energy from an external heat source into useful electric and/or mechanical energy, where the method includes the steps of transforming thermal energy from a fully vaporized higher pressure stream into a usable energy form to product a spent higher pressure stream and transforming thermal energy from a vaporized lower pressure stream into a usable energy form to product a spent lower pressure stream. The method further includes the steps of heating a higher pressure liquid stream with a portion of a spent higher pressure stream to form a heated higher pressure stream and a first partially condensed spent higher pressure stream and heating a lower pressure stream with a remaining portion of the spent higher pressure stream to form a heated lower pressure stream and a second partially condensed spent higher pressure stream. The method also includes the steps of heating the heated higher pressure liquid stream with a portion of an external heat source stream to form a hotter higher pressure stream and a first spent external heat source stream and heating the heated lower pressure stream with a remaining portion of the external hear source stream to form a vaporized lower pressure stream and a second spent external heat source stream. The method also includes the steps of heating the hotter higher pressure stream with the external heat source stream to form the fully vaporized higher pressure stream, separating the partially condensed spent higher pressure streams into a spent higher pressure liquid stream and a spent higher pressure vapor stream, mixing the spent higher pressure liquid stream with the spent lower pressure stream at the pressure of the spent lower pressure stream to form a combined spent lower pressure stream and condensing the combined spent lower pressure stream with an external cooling stream to form a condensed spent lower pressure stream. The method further includes the steps of mixing the condensed spent lower pressure stream with the spent higher pressure vapor stream to form a combined partially condensed spent higher pressure stream at the pressure of the spent higher pressure vapor stream, condensing the combined partially condensed spent high pressure stream to form a fully condensed liquid stream; and forming the higher pressure stream and the lower pressure stream from a fully condensed liquid stream.
The present invention also provides a method for improved energy conversion of heat from external heat sources including the steps of forming a higher pressure working fluid stream and a lower pressure working fluid stream from a fully condensed working fluid stream. After the two streams are formed, the higher pressure working fluid stream is heated with a portion of a spent higher pressure working fluid stream to form a heated higher pressure working fluid stream and a first partially condensed spent higher pressure working fluid stream, the heated higher pressure working fluid stream is heated with a portion of a partially cooled external source stream to form a hotter higher pressure working fluid stream and a first spent external source stream and finally the hotter higher pressure working fluid stream is vaporized with an external source stream to form a fully vaporized higher pressure working fluid stream and the partially cooled external source stream. Once fully vaporized, the thermal energy from the fully vaporized higher pressure working fluid stream is transformed into a usable energy form to product a spent higher pressure working fluid stream. While the higher pressure stream is being processed, the lower pressure, working fluid stream is heated with a remaining portion of the spent higher pressure working fluid stream to form a heated lower pressure working fluid stream and a second partially condensed spent higher pressure working fluid stream, and the heated lower pressure working fluid stream is heated with a remaining portion of the partially cooled external source stream to form a vaporized lower pressure working fluid stream and a second spent external source stream. Once vaporized, the thermal energy from the vaporized lower pressure working fluid stream is transformed into a usable energy form to product a spent lower pressure working fluid stream. The first and second partially condensed, spent higher pressure working fluid streams are separated into a spent higher pressure liquid working fluid stream and a higher pressure vapor working fluid stream and the spent lower pressure working fluid stream is mixed with the spent higher pressure liquid working fluid stream at the lower pressure to form a combined spent lower pressure working fluid stream. The combined spent lower pressure working fluid stream is cooled with an external cooling stream to form a condensed lower pressure working fluid stream, while the condensed lower pressure working fluid stream and the spent higher pressure vapor working fluid stream at a pressure of the spent higher pressure vapor working fluid stream is cooled with another external cooling stream to form the fully condensed working fluid stream.
The present invention also provides an apparatus for improved conversion of thermal energy into mechanical and/or electrical energy including a first means for expanding a fully vaporized higher pressure stream, transferring its energy into usable form and producing a higher pressure spent stream and a second means for expanding a fully vaporized lower pressure stream, transferring its energy into usable form and producing a lower pressure spent stream. The apparatus also includes a first heat exchanger adapted to condense a combined lower pressure spent stream with an external coolant stream to form a condensed combined lower pressure spent stream, a first pump adapted to increase a pressure of the condensed combined lower pressure spent stream to form an increased pressure, condensed combined lower pressure spent stream, and a first stream mixer adapted to combine the increased pressure, condensed combined lower pressure spent stream and a vapor higher pressures spent stream to form a partially condensed stream. The apparatus also includes a second heat exchanger adapted to condense the partially condensed stream with an external coolant stream to form a fully condensed liquid stream and a first stream splitter adapted to form first and second portions of the fully condensed liquid stream. The apparatus also includes a second pump adapted to increase a pressure the first portion of the fully condensed liquid stream to form a higher pressure liquid stream and a third pump adapted to increase a pressure the second portion of the fully condensed liquid stream to form a lower pressure liquid stream. The apparatus also includes a third heat exchanger adapted to heat the higher pressure liquid stream with a first portion of a higher pressure spent stream to form a heated higher pressure liquid stream and a first partially condensed higher pressure spent stream and a fourth heat exchanger adapted to heat the lower pressure liquid stream with a remaining portion of the higher pressure spent stream to form a heated lower pressure liquid stream and a second partially condensed higher pressure spent stream. The apparatus also includes a fifth heat exchanger adapted to heat the heated higher pressure liquid stream with a first portion of a partially cooled external heat source stream to form a hotter higher pressure liquid stream and a first spent external heat source stream and a sixth heat exchanger adapted to heat the heated lower pressure liquid stream with a remaining portion of the partially cooled external heat source stream to form a vaporized lower pressure stream and a second spent external heat source stream. The apparatus also includes a seventh heat exchanger adapted to vaporize the hotter higher pressure liquid stream with an external heat source stream mixer to form the fully vaporized higher pressure stream and the partially cooled external heat source stream. The apparatus also includes a second stream splitter adapted to form the first and second portions of the higher pressure spent stream, a third stream splitter adapted to form the first and second portions of the cooled external heat source stream, a second stream mixer adapted to combine the first and second partially condensed higher pressure spent stream to form a combined partially condensed higher pressure spent stream, a gravity separator adapted to separate combined partially condensed higher pressure spent stream into a lean liquid stream and a rich vapor stream, a throttle valve adapted to change the pressure of the lean liquid stream to a pressure of the lower pressure spent stream and a third stream mixer adapted to combine the pressure adjusted lean liquid stream with the lower pressure spent stream. The apparatus is capable of achieving improved efficiency due to the mixing of the lean liquid stream with the spent lower pressure stream so that the combined stream can be condensed at a lower pressure than a non-lean stream.